The FBI has identified an employee of a federal contracting firm suspected of being the so-called "second leaker" who turned over sensitive documents about the U.S. government's terrorist watch list to a journalist closely associated with ex-NSA contractor Edward Snowden, according to law enforcement and intelligence sources who have been briefed on the case.

The FBI recently executed a search of the suspect's home, and federal prosecutors in Northern Virginia have opened up a criminal investigation into the matter, the sources said.

But the case has also generated concerns among some within the U.S. intelligence community that top Justice Department officials — stung by criticism that they have been overzealous in pursuing leak cases — may now be more reluctant to bring criminal charges involving unauthorized disclosures to the news media, the sources said. One source, who asked not to be identified because of the sensitivity of the matter, said there was concern "there is no longer an appetite at Justice for these cases."

Marc Raimondi, a spokesman for the Justice Department, declined to comment on the investigation into the watch-list leak, citing department rules involving pending cases.

As for the department's overall commitment to pursue leak cases, he added: "We're certainly going to follow the evidence wherever it leads us and take appropriate action."

Another source familiar with the case said: "Investigators are continuing to pursue it, but are not ready to charge yet."

The case in question involves an Aug. 5 story published by The Intercept, an investigative website co-founded by Glenn Greenwald, the reporter who first published sensitive NSA documents obtained from Snowden.

The story, co-authored by Jeremy Scahill and Ryan Devereaux, was accompanied by a document "obtained from a source in the intelligence community" providing details about the watch-listing system that were dated as late as August 2013, months after Snowden fled to Hong Kong and revealed himself as the leaker of thousands of top secret documents from the NSA.

This prompted immediate speculation that there was a "second leaker" inside the U.S. intelligence community providing material to Greenwald and his associates.

That point is highlighted in the last scene of the new documentary about Snowden released this weekend, called "Citizenfour," directed by filmmaker Laura Poitras, a co-founder with Greenwald and Scahill of The Intercept.

Greenwald tells a visibly excited Snowden about a new source inside the U.S. intelligence community who is leaking documents. Greenwald then scribbles notes to Snowden about some of the details, including one briefly seen about the U.S. drone program and another containing a reference to the number of Americans on the watch list.

"The person is incredibly bold," Snowden says. Replies Greenwald: "It was motivated by what you did."

In an interview on the radio show "Democracy Now," Scahill, who also briefly appears in "Citizenfour," says the new source described in the film provided him with a document that "outlines the rulebook for placing people on a variety of watch lists." The source is "an extremely principled and brave whistleblower" who made his disclosures "at great personal risk," Scahill says in the interview.

Contacted Monday, Scahill declined any comment about his source, but said neither he nor The Intercept had been notified by federal officials about the investigation. He added, however, that he is not surprised to learn of the probe: "The Obama administration in my view is conducting a war against whistleblowers and ultimately against independent journalism."

John Cook, editor of The Intercept, said the website's stories had revealed "crucial information" about the excesses of the U.S. watch-listing system. "Any attempt to criminalize the public release of those stories benefits only those who exercise virtually limitless power in secret with no accountability," he told Yahoo News.

Sources familiar with the investigation say the disclosures prompted the National Counterterrorism Center to file a "crimes report" with the Justice Department — an official notification that classified material has been compromised and a violation of federal law may have taken place.

The documents in question disclose multiple details about how federal intelligence agencies provide entries and track suspects on the Terrorist Identities Datamart Environment, or TIDE — a master database with over 1 million names that provides the basis for watch-listing individuals and placing them on "no fly" lists when there are sufficient links to terrorism.

Citizenfour movie poster. (Radius TWC)

One document is stamped as "Secret" and "NOFORN," meaning it cannot be shared with foreign governments. These, however, are far less sensitive than some of the NSA materials leaked by Snowden.

But the Obama administration's aggressive anti-leak efforts triggered a firestorm of criticism last year after disclosures that, in pursuing these cases, prosecutors had secretly subpoenaed phone records from the Associated Press and filed a search warrant identifying a Fox News reporter as a potential "co-conspirator" under the Espionage Act for his efforts to coax information from a confidential source.

Since September of last year, when a former FBI agent pleaded guilty to disclosing details about an al-Qaida bomb plot to the AP, the Justice Department has brought no further leak cases. Attorney General Eric Holder — who sources say was personally stung by the criticism — has also unveiled new "guidelines" that restrict how the Justice Department would seek information from the news media in leak cases.

Holder, who recently announced his plans to step down, also appeared to signal that he was eager to avoid further confrontations with the press when he was asked whether he would seek to incarcerate New York Times reporter James Risen if he refused to testify in an upcoming trial of a former CIA officer accused of leaking him information about a covert effort to disrupt Iran's nuclear program. Risen has vowed he will never testify about a confidential source.

But Steve Aftergood, who closely tracks government secrecy efforts, said, "It's an open question at this point whether the administration will indict any other leakers or pursue other prosecutions."

He noted that, despite Holder's comments, Justice Department prosecutors had yet to formally inform a federal judge whether they will call Risen at the trial of the former CIA officer — a move that could result in a direct confrontation with the reporter if he is asked to identify his source.

"These leaks are taken extremely seriously," he said. If prosecutors have sufficient evidence against the suspected new leaker, "I don't think they will let it slide."